Degree Type

Dissertation

Date of Award

2018

Degree Name

Doctor of Philosophy

Department

Plant Pathology and Microbiology

Major

Genetics and Genomics

First Advisor

Nick Lauter

Second Advisor

Alison Robertson

Abstract

Plant diseases account for more than 40% of crop losses. Breeding for disease resistance is the most effective means of crop protection against these losses. Disease resistance in plants is categorized into qualitative and quantitative resistance. Qualitative disease resistance is controlled by single major genes that confer complete or near complete resistance against disease pathogens. However, the absence or instability of qualitative resistance in many crop-pathogen interaction systems has necessitated a shift in research toward quantitative disease resistance (QDR). QDR is conditioned by several genes of minor effects resulting in reduced levels of disease. The multigenic nature of QDR overcomes the limitations of qualitative disease resistance. As a fairly new field of research, the specific mechanisms underlying the genetic architecture of QDR in response to pathogen attack are still not well understood. The goal of this research was to identify and characterize the genetic, molecular and mechanistic bases of QDR in maize against hemi-biotrophic Setosphaeria turcica, the causative agent of Northern leaf blight (NLB). The unique lifestyle of Setosphaeria turcica, as well as the sequenced and annotated maize genome provide an opportunity to study the quantitative nature of host-hemi-biotrophic interactions.

This research employed both phenotypic and genetic approaches to elucidate the mechanisms that underlie QDR with the aim of improving plant health and production. A new genetic map for the Intermated B73 x Mo17 Syn10 doubled haploid line (IBMSyn10DHL) population was created and evaluated. To identify and characterize the genetic basis of quantitative disease resistance in maize-S. turcica interaction, IBMDHLs were tested against two isolates of Setosphaeria turcica across multiple environments. Unique and overlapping NLB resistance-related QTL were identified within and across environments respectively. Additionally, IBMDHL and their backcross hybrid populations were tested in Iowa against Iowa NLB isolate to estimate the genetic mode of action of loci underlying quantitative disease resistance. Results from this research highlighted the multigenic nature and specificity of QDR and the genetic effects of genes underlying QDR. Furthermore, previously reported and novel disease resistance-related QTL were identified.

Copyright Owner

Mercy Kasuzi Kabahuma

Language

en

File Format

application/pdf

File Size

156 pages

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